Plasma processing apparatus and method therefor

ABSTRACT

A dry etching apparatus plasma processes a wafer held by a carrier having a frame and an holding sheet. A electrode unit of a stage includes an electrostatic chuck. Adjacent to an upper surface of the electrostatic chuck, a first electrostatic attraction electrode and a second electrostatic attraction electrode are incorporated. The first electrostatic attraction electrode is of unipolar type and electrostatically attracts the wafer via the holding sheet. The second electrostatic electrode is of bipolar type and electrostatically attracts the frame via the holding sheet as well as a holding sheet between the wafer and the frame. Both of plasma processing performance and electrostatic attraction performance are improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of Japanese Patent Application No.2013-228097 filed on Nov. 1, 2013, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a plasma processing apparatus and amethod therefor.

Description of Related Art

The plasma processing apparatuses disclosed in Japanese Patent No.4858395 and United States Patent Application Publication No.2012/0238073 have process targets of a substrate (wafer, for example)held in a carrier including an annular frame and a holding sheet. Thesubstrate is held on a holding sheet. In addition, these plasmaprocessing apparatuses include a cover that covers a frame and an areabetween the substrate outer-periphery of the holding sheet and the frameso that the frame and the area are not to be exposed to the plasma.

The cover is heated by being exposed to plasma, and tends to have a hightemperature. Radiant heat from the heated cover gives thermal damage tothe resist of the substrate outer peripheral part, holding sheet, andframe. As measures against the thermal damage by the radiant heat fromsuch a cover, the substrate and the carrier are electrostaticallyattracted to and brought into close contact with the stage (cooled bycoolant circulation), and can be cooled by the heat transfer to thestage.

In the conventional plasma processing apparatus, when the target of theplasma process is a substrate held by the carrier, there has not beenany specific study on in what manner the electrostatic attraction shouldbe performed so that the plasma process performance and theelectrostatic attraction performance (cooling performance) can becompatible.

SUMMARY OF THE INVENTION

The present invention has an object to improve both the plasma processperformance and the electrostatic attraction performance in a plasmaprocessing apparatus for plasma-processing the substrate held by thecarrier.

A first aspect of the present invention provides a plasma processingapparatus for plasma processing a substrate held by a carrier having aframe, and a holding sheet, comprising, a chamber having a pressurereducible internal space, a process gas supply section configured tosupply a process gas into the internal space, a pressure reducingsection configured to reduce pressure of the internal space, a plasmagenerating section configured to generate plasma in the internal space,a stage provided in the chamber and including an electrode unit on whichthe carrier is placed, a first electrostatic attraction electrode ofunipolar type incorporated in a first area of the electrode unit, thefirst area being an area in which the substrate is placed via theholding sheet, and a second electrostatic attraction electrode ofbipolar type which is incorporated in a second area of the electrodeunit and to which a direct current voltage is applied, the second areaincluding at least an area in which the frame is placed via the holdingsheet and an area in which the holding sheet between the substrate andthe frame is placed.

Specifically, the plasma processing apparatus further comprises acooling section configured to cool the electrode unit.

More specifically, the plasma processing apparatus further comprising acover capable of coming into and out of contact with stage. The covercomprises a body covering the holding sheet and the frame of the carrierplaced on the electrode unit, and a window formed to penetrate the bodyin a thickness direction so as to expose the substrate held in thecarrier placed on the electrode unit to the internal space.

The substrate is electrostatically attracted by the first electrostaticattraction electrode of unipolar type. A electrostatic attraction forceof the unipolar-type electrostatic attraction electrode is weaker thanthat of the bipolar-type. However, the unipolar-type electrostaticattraction electrode is superior to the bipolar-type in term of theplasma processing performance due to that a whole surface of thesubstrate can be equally attracted. For example, in the case of plasmadicing, both the attraction force fluctuation of the before and after ofsingulating the substrate and the difference of the localized attractionforce of unipolar type are less than those of bipolar type. In addition,specifically, in the case of the process (Si etching process, forexample) where the radical reaction of the high plasma density and thelow bias power are dominant, with the change of the bias power of thebefore and after of singulating the substrate, the pattern of theelectrostatic attraction electrode of bipolar type may be transcribed tothe substrate side. On the other hand, the frame and the holding sheet(between the substrate and the frame) are electrostatically attracted tothe electrode unit by the second electrostatic attraction electrode ofbipolar type. The electrostatic attraction electrode of bipolar type isinferior to that of unipolar type in terms of the plasma processperformance, but is stronger than that of unipolar type in terms of theelectrostatic attraction force. That is, in the present invention, thefirst electrostatic attraction electrode of unipolar type is used forthe electrostatic attraction of the substrate which directly influencesthe plasma process performance, on the other hand, the secondelectrostatic attraction electrode of bipolar type with the strongelectrostatic attraction force is used for the frame and the holdingsheet with less influence on the plasma process performance than thesubstrate. As a result, both the plasma process performance and theelectrostatic attraction performance can be improved. With theimprovement of the electrostatic attraction performance, the holdingsheet and the frame are cooled effectively by the heat transfer to thestage, and the damage caused by the radiant heat from the cover can bereduced effectively.

The second electrostatic attraction electrode may electrostaticallyattract the cover. In this structure, the second area includes an areain which the cover comes into contact with the electrode unit.

Alternatively, the second electrostatic attraction electrode does notelectrostatically attract the cover. In this structure, the second areadoes not include the area in which the cover comes into contact with theelectrode unit, and a clamp mechanism for pressing the cover onto thestate is provided.

A direct current voltage can be applied to the first electrostaticattraction electrode. Alternatively, a voltage obtained by superimposinga radio frequency voltage on a direct current voltage can be applied tothe first electrostatic attraction electrode.

A second aspect of the present invention provides a method for plasmaprocessing a substrate held by a carrier having a frame and a holdingsheet. The method comprises loading the carrier holding the substrateinto a chamber of a plasma processing apparatus so that the carrier isplaced on an electrode unit of a stage, electrostatically attracting thesubstrate by a first electrostatic attraction electrode of unipolar typeincorporated in the electrode unit, electrostatically attracting atleast the frame and the holding sheet by a second electrostaticattraction electrode of bipolar type incorporated in the electrode unit,and generating plasma in the chamber, thereby plasma processing thesubstrate.

According to the invention, the first electrostatic attraction electrodeof unipolar type is used for the electrostatic attraction of thesubstrate, whereas the second electrostatic attraction electrode ofbipolar type is used for the electrostatic attraction of the frame andthe holding sheet. This improves both of plasma processing performanceand electrostatic attraction performance.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome apparent from the following description taken in conjunction withpreferred embodiments thereof with reference to the accompanyingdrawings, in which:

FIG. 1 is a sectional view of a plasma processing apparatus according toa first embodiment of the present invention (a cover is at a loweredposition);

FIG. 2 is a partial enlarged view of FIG. 1;

FIG. 3 is a plane view of a carrier arranged on a stage and the covercovering the carrier;

FIG. 4 is a partial enlarged view of first and second electrostaticattraction electrodes;

FIG. 5 is a sectional view of the plasma processing apparatus accordingto the first embodiment of the present invention (the cover is at araised position);

FIG. 6 is a partial sectional view of a plasma processing apparatusaccording to a second embodiment of the present invention; and

FIG. 7 is a partial sectional view of a plasma processing apparatusaccording to a third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, an embodiment of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription, terms indicating particular directions and positions(including such terms as “upper”, “lower”, “side”, and “end”) aresometimes used. The use of these terms are intended to facilitate theunderstanding of the present invention with reference to the drawings,and the technical scope of the present invention is not limited by themeaning of these terms. In addition, the following description is merelyexemplary in nature, and it is not intended to limit the presentinvention, the application thereof, and the use thereof.

First Embodiment

FIGS. 1 to 4 show a dry etching apparatus 1 which is an example of aplasma processing apparatus according to an embodiment of the presentinvention. In this embodiment, plasma dicing is performed on a wafer(substrate) 2 by this dry etching apparatus 1. Plasma dicing is a methodof cutting, by using a dry etching boundary line (street), the wafer 2in which a plurality of IC units (semiconductor devices) are formed, anddividing the wafer 2 into individual IC units. Referring to FIG. 2, thewafer 2 having a circular shape in this embodiment includes a front face2 a on which IC units, etc., not shown in the figure, are formed, and aback face 2 b (on which IC units, etc. are not formed) on the oppositeside of the front face 2 a. On the front face 2 a of the wafer 2, a mask(not shown in the figure) is formed in a pattern for plasma dicing.

Referring to FIG. 1, the dry etching apparatus 1 includes a chamber(vacuum vessel) 3 which has a pressure reducible internal space. Acarrier 4 can be accommodated in the internal space through a gate 3 aof the chamber 3.

Referring to FIGS. 2 and 3, the carrier 4 includes a holding sheet 5which detachably holds the wafer 2. As for the holding sheet 5, forexample, a UV tape can be used. The UV tape is extendable and holds thewafer 2 by its adhesive force. However, the chemical properties of theUV tape are changed and the adhesive force is greatly reduced byirradiation of ultraviolet rays. The holding sheet 5 has an adhesiveface 5 a on one face, and a non-adhesive face 5 b on the other face. Theholding sheet 5 is flexible, flexes easily, and cannot maintain aconstant shape only by itself. Therefore, on the adhesive face 5 a nearthe outer peripheral edge of the holding sheet 5, an approximatelyannular thin frame 6 is adhered. The frame 6 is made of, for example,metal such as stainless steel, and aluminum, or resin, and has arigidity that can hold the shape together with the holding sheet 5. Inthe holding sheet 5 in the carrier 4, the wafer 2 is held by the backface 2 b being adhered on the adhesive face 5 a.

Referring to FIG. 1, above the dielectric wall 7 that closes the toppart of the chamber 3 of the dry etching apparatus 1, an antenna 8 isdisposed as an upper part electrode. The antenna 8 is electricallyconnected to a first high frequency power source 9A. The antenna 8 andthe first radio frequency power source 9A constitute a plasma generatingsection. On the bottom part side of the chamber 3, a stage 11 isdisposed on which the carrier 4 holding the wafer 2 is placed. The gasinlet port 7 a, which is formed in the dielectric wall 7, to theinternal space of chamber 3 is connected to a process gas source 10. Tothe exhaust port 3 b of the chamber 3, a pressure reducing mechanism 12including a vacuum pump for evacuating the internal space is connected.

Referring to FIGS. 1 and 2, the stage 11 includes an electrode unit 13,a base section 14 supporting the electrode unit 13, and an exterior unit15 surrounding the outer periphery of the electrode unit 13 and the basesection 14. The exterior unit 15 is made of a ground shielding material(metal having conductivity and etching resistance). The exterior unit 15protects the electrode unit 13 and the base section 14 from the plasma.A cooling device 16 is disposed in the stage 11.

The electrode unit 13 includes an electrostatic chuck 17 constitutingthe top layer of the stage 11, and an electrode unit body 18 made ofmetal such as aluminum alloy and disposed on the lower side of theelectrostatic chuck 17.

The electrostatic chuck 17 of the electrode unit 13 is made of thinceramics, sprayed ceramics, or a sheet (tape) of dielectric material.The carrier 4 holding the wafer 2 is placed on the central part of theupper face of the electrostatic chuck 17. In addition, on the outerperipheral side part of the electrostatic chuck 17, a cover 19 describedbelow is placed. In the electrode unit 13, first and secondelectrostatic attraction electrodes 24 and 25 and a bias electrode 27are incorporated. The details of the electrostatic chuck 17 be describedlater.

The cooling device (cooling section) 16 includes a coolant flow path 18a formed in the electrode unit body 18, and a coolant circulation device21. The coolant circulation device 21 performs cooling by circulatingthe temperature-adjusted coolant in the coolant flow path 18 a, andmaintains the electrode unit 13 at a desired temperature.

The carrier 4 is placed on the electrode unit 13 of the stage 11 withthe face holding the wafer 2 of the holding sheet 5 (adhesive face 5 a)in an upward posture, and the non-adhesive face 5 b of the holding sheet5 comes into contact with the upper face of the electrode unit 13. Thecarrier 4 is placed in a predetermined position and posture with respectto the electrostatic chuck 17 of the electrode unit 13 by a conveyancemechanism not shown in the figure. Hereinafter, this predeterminedposition and posture are referred to as “normal position”.

The carrier 4 placed in the normal position is lifted by the first driverod 22A and unloaded after the plasma process (See FIG. 5). The firstdrive rod 22A is vertically driven by the first drive mechanism 23Ashown conceptually only in FIGS. 1 and 5. Specifically, the carrier 4 ismade to move to the raised position shown in FIG. 5, and the loweredposition shown in FIG. 1.

Referring to FIGS. 1 to 3, a cover 19 which moves up and down on theupper side of the stage 11 is disposed in the chamber 3. The cover 19includes a body 19 a having a thin circular outer contour, and a window19 b formed at the center of the body 19 a so as to penetrate in thethickness direction. On the lower face of the body 19 a, an annularprotrusion portion 19 c is formed so as to abut on the upper face of theelectrostatic chuck 17 of the electrode unit 13 when the body 19 a islowered. The lower face of the annular protrusion portion 19 c includesan annular contact face 19 d having a predetermined width dimension in aradial direction. The cover 19 (body 19 a) is made of a material such asa metal material including aluminum or aluminum alloy or the like,silicon carbide, aluminum nitride, and a ceramic material with excellentthermal conductivity.

The outer diameter dimension of the body 19 a of the cover 19 is formedto be sufficiently larger than the outer contour of the carrier 4. Thereason why the body 19 a covers the frame 6 and the holding sheet 5(area between the outer peripheral part of the wafer 2 and the frame 6)of the carrier 4 during the plasma process is to protect the frame 6 andthe holding sheet 5 from the plasma. The diameter of the window 19 b ofthe cover 19 is set, for example, in the range of ±2 mm with respect tothe outer diameter dimension of the wafer 2. During the plasma process,the wafer 2 is exposed to the internal space of the chamber 3 throughthe window 19 b.

The vertical movement operation of the cover 19 is performed by a seconddrive rod 22B connected to the body 19 a. The second drive rod 22B isvertically driven by a second drive mechanism 23B shown conceptuallyonly in FIGS. 1 and 5. The cover 19 is raised and lowered by thevertical movement of the second drive rod 22B. Specifically, the cover19 can move to the raised position shown in FIG. 5 and the loweredposition shown in FIG. 1.

Referring to FIG. 5, the cover 19 in the raised position is located witha sufficient distance above the stage 11. Thus, when the cover 19 is inthe raised position, it is possible to perform the operation to load thecarrier 4 (holding the wafer 2) on the upper face of the electrostaticchuck 17 of the electrode unit 13, and oppositely the operation tounload the carrier 4 from the upper face of the electrode unit 13.

Referring to FIGS. 1 and 2, the cover 19 in the lowered position coversthe holding sheet 5 (except the part holding the wafer 2) and the frame6 in the carrier 4 in the normal position. In addition, when the cover19 is in the lowered position, the lower face of annular protrusionportion 19 c (the above-described contact face 19 d) abuts on the upperface of the electrostatic chuck 17 of the electrode unit 13. That is,the second drive mechanism 23B functions as a means for raising andlowering the cover 19 with respect to the stage 11, and also functionsas a means for making the cover 19 come into and out of contact with thestage 11.

In the following, referring to FIGS. 1 and 2, the electrostatic chuck 17of the electrode unit 13 will be described. In the followingdescription, unless specifically mentioned, the carrier 4 holding thewafer 2 is assumed to be in the normal position (a state of being placedon the electrostatic chuck 17 in a predetermined position and posture).

In this embodiment, a whole of the upper face of the electrostatic chuck17 (including an area on which the carrier 4 is placed and an area ontowhich the annular protrusion portion 19 c of the cover 19 abuts) issubstantially flat. Here, the term “substantially flat” means that itcan be regarded as a flat surface except for a fine front-face roughnessand unavoidable factors such as manufacturing tolerances.

In the electrostatic chuck 17, in an adjacent area of the upper face ofthe central part, that is, the area in which the wafer 2 is placed viathe holding sheet 5 (first area A1), a first electrostatic attractionelectrode 24 of unipolar type is incorporated. As shown in FIG. 4, thefirst electrostatic attraction electrode 24 in this embodiment has athin circular-disc shape with an outer diameter slightly larger than thewafer 2. A first DC power source 26A is electrically connected to thefirst electrostatic attraction electrode 24.

In the electrostatic chuck 17, a second electrostatic attractionelectrode 25 of bipolar type is incorporated in an adjacent area of theupper face in the outer peripheral part surrounding the central part.Specifically, the second electrostatic attraction electrode 25 isincorporated in an area (second area A2) including an area in which theframe 6 is placed via the holding sheet 5, an area (indicated by areference sign A3 in FIG. 2) in which the holding sheet 5 between thewafer 2 and the frame 6 is placed, and an area (indicated by a referencesign A4 in FIG. 2) in which the annular protrusion portion 19 c of thecover 19 in the lowered position abuts. As shown in FIG. 4, the secondelectrostatic attraction electrode 25 includes an endless-shapedpositive electrode 25 a surrounding the first electrostatic attractionelectrode 24, and an endless-shaped negative electrode 25 b disposedoutside the positive electrode 25 a. The positive electrode 25 a iselectrically connected to the positive electrode of a second DC powersource 26B, and the negative electrode 25 b is electrically connected tothe negative electrode of the second DC power source 26B. In thisembodiment, both the positive electrode 25 a and the negative electrode25 b of the second electrostatic attraction electrode have strip shapesthat meander with constant widths.

In the electrostatic chuck 17, a bias electrode 27 (RF electrode) isincorporated below the first electrostatic attraction electrode 24. Thebias electrode 27 is electrically connected to the second radiofrequency power source 9B for applying a bias voltage.

The controller 28 schematically shown in FIGS. 1 and 5 controls theoperation of the each element which constitutes the dry etchingapparatus 1. These elements include the first and second radio frequencypower sources 9A and 9B, the process gas source 10, the pressurereducing mechanism 12, the first and second dc power sources 26A and26B, the coolant circulation device 21, and the first and second drivemechanisms 23A and 23B.

Next, the operation of the dry etching apparatus 1 in this embodimentwill be described.

First, the carrier 4 where the wafer 2 is adhered in the center of theholding sheet 5 is loaded to the internal space of the chamber 3, andplaced in the normal position on the electrostatic chuck 17 by theconveyance mechanism not shown in the figure. In this case, the cover 19is in the raised position (FIG. 5).

The second drive rod 22B is driven by the second drive mechanism 23B,and the cover 19 is lowered from the raised position (FIG. 5) to thelowered position (FIG. 1). When the cover 19 is in the lowered position,the frame 6 and the holding sheet 5 (the area between the wafer 2 andthe frame 6) of the carrier 4 are covered with the cover 19, and thewafer 2 is exposed through the window 19 b. In addition, the lower faceof the annular protrusion portion 19 c of the cover 19 (contact face 19d) comes into contact with the upper face of the electrostatic chuck 17(an area indicated by the reference sign A4 in FIG. 2).

A direct current voltage is applied from the first DC power source 26Ato the first electrostatic attraction electrode 24 of unipolar type, andthe wafer 2 is held on the upper face of the electrostatic chuck 17 viathe holding sheet 5 by the electrostatic attraction. In addition, adirect current voltage is applied from the second DC power source 26B tothe second electrostatic attraction electrode 25 of bipolar type, andthe frame 6 and the holding sheet 5 (the area between the wafer 2 andthe frame 6) are held on the upper face of the electrostatic chuck 17 bythe electrostatic attraction. In addition, by applying a direct currentvoltage from the second DC power source 26B to the bipolar secondelectrostatic attraction electrode 25, the cover 19 is electrostaticallyattracted to the upper face of the electrostatic chuck 17. In otherwords, the cover 19 is pressed onto the upper face of the electrostaticchuck 17 by the electrostatic attraction force.

Next, the process gas for plasma dicing is introduced to the chamber 3from the process gas source 10, and at the same time, discharged by thepressure reducing mechanism 12 to maintain the inside of the chamber 3at a predetermined pressure. After that, radio frequency power issupplied to the antenna 8 from the first radio frequency power source 9Ato generate plasma inside the chamber 3, and the generated plasma isapplied to the wafer 2 exposed through the window 19 b of the cover 19.In this case, a bias voltage is applied from the second radio frequencypower source 2B to the bias electrode 27. In addition, the coolingdevice 16 cools the stage 11 including the electrode unit 13. A part ofthe wafer 2, the part exposed through the mask (street), is removed inthe front face 2 a to the back face 2 b by physicochemical action ofradicals and ions in the plasma, and the wafer 2 is divided intoindividual chips (individual pieces).

During the plasma dicing, the cover 19 is heated by exposure to plasma.However, the cover 19 is made of a material having high thermalconductivity, and the annular protrusion portion 19 c is pressed ontothe upper face of the electrostatic chuck 17 by the electrostaticattraction of the second electrostatic attraction electrode 25.Therefore, the heat generated in the cover 19 can be released to thestage 11 cooled by the cooling device 16. In other words, during theplasma dicing, the cover 19 is cooled by the heat conduction to thestage 11.

During the plasma dicing, the wafer 2 is electrostatically attracted tothe upper face of the electrostatic chuck 17 by the first electrostaticattraction electrode 24 via the holding sheet 5. Further, during theplasma dicing, the frame 6 and the holding sheet 5 are electrostaticallyattracted to the upper surface of the electrostatic chuck 17 by thesecond electrostatic attraction electrode 25. Therefore, during theplasma dicing, the heat generated in the wafer 2, the frame 6, and theholding sheet 5 can be released to the stage 11 cooled by the coolingdevice 16. In other words, during the plasma dicing, the wafer 2, theframe 6, and the holding sheet 5 are cooled by the heat conduction tothe stage 11.

As described above, the cover 19 itself heated by being exposed toplasma is cooled by the heat transfer to the stage 11, and in addition,the wafer 2, the frame 6, and the holding sheet 5 are also cooled by theheat transfer to the stage 11, and thereby, the thermal damage to thecarrier 4 (sheet, frame, and wafer) by the radiant heat from the cover19 can be effectively prevented.

After the plasma dicing, the second drive rod 22B is driven by thesecond drive mechanism 23B, and the cover 19 is moved from the loweredposition to the raised position. Then, the first drive rod 22A is drivenby the first drive mechanism 23A, the carrier 4 is moved from thelowered position to the raised position, and the carrier 4 is conveyedfrom the chamber 3 by the conveyance mechanism not shown in the figure.

In this embodiment, as described above, the first electrostaticattraction electrode 24 of unipolar type is used for the electrostaticattraction of the wafer 2, on the other hand, the second electrostaticattraction electrode 25 of bipolar type is used for the electrostaticattraction of the carrier 4 (the frame 6 and the holding sheet 5) andthe cover 19. This improves both the plasma process performance and theelectrostatic attraction performance. In the following, the details onthis point will be described.

The wafer 2 is electrostatically attracted to the electrostatic chuck 17by the first electrostatic attraction electrode 24 of unipolar type. Theelectrostatic attraction electrode of unipolar type electrostaticallyattracting mainly by Coulomb force has a weaker electrostatic attractionforce than that of bipolar type. However, the electrostatic attractionelectrode of unipolar type can uniformly attract the entire face of thewafer, and therefore, in terms of the plasma process performance, theelectrostatic attraction electrode of unipolar type is superior to thatof bipolar type which performs electrostatic attraction byJohnsen-Rahbeck force due to the current mainly flowing through the backface of the holding sheet 5 and the wafer 2. For example, in the case ofplasma dicing, both the attraction force fluctuation of the before andafter of singulating the wafer 2 and the difference of the localizedattraction force of unipolar type are less than those of bipolar type.In addition, specifically, in the case of the process (Si etchingprocess, for example) where the radical reaction of the high plasmadensity and the low bias power are dominant, with the change of the biaspower of the before and after of singulating the wafer 2, the pattern ofthe electrostatic attraction electrode of bipolar type may betranscribed to the substrate side. On the other hand, the frame 6 andthe cover 19 are electrostatically attracted to the electrostatic chuck17 by the second electrostatic attraction electrode 25 of bipolar type.The electrostatic attraction electrode of bipolar type is inferior tothat of unipolar type in terms of the plasma process performance, but isstronger than that of unipolar type in terms of the electrostaticattraction force. That is, in the present invention, the firstelectrostatic attraction electrode 24 of unipolar type is used for theelectrostatic attraction of the wafer 2 which directly influences theplasma process performance, on the other hand, the second electrostaticattraction electrode 25 of bipolar type with the strong electrostaticattraction force is used for the conveyance frame 6 and the cover 19with less influence on the plasma process performance than the wafer 2.As a result, both the plasma process performance and the electrostaticattraction performance can be improved. With the improvement of theelectrostatic attraction performance, the carrier 4 and the cover 19 arecooled effectively by the heat transfer to the stage, and the damagecaused by the radiant heat from the cover 19 can be reduced effectively.

In the following, other embodiments of the present invention will bedescribed. The configuration and the operation not specificallymentioned in the description of these embodiments are the same as thoseof the first embodiment.

Second Embodiment

In the second embodiment shown in FIG. 6, the bias electrode 27 and thesecond radio frequency power source 9B are eliminated, and a voltageobtained by superimposing a radio frequency voltage as a bias voltage ona direct current voltage is applied from the power source 29 to thefirst electrostatic attraction electrode 24. By eliminating the secondradio frequency power source 9B, the configuration of the electrostaticchuck 17 can be simplified.

Third Embodiment

In the third embodiment shown in FIG. 7, the second electrostaticattraction electrode 25 is disposed only in the area including the areain which the frame 6 is placed via the holding sheet 5 and the area inwhich the holding sheet 5 between the wafer 2 and the frame 6 is placedon the electrostatic chuck 17. In other words, the second electrostaticattraction electrode 25 is not disposed in the area (indicated by thereference sign A4 in FIG. 7) in which the cover 19 in the loweredposition abuts onto the electrostatic chuck 17, and the cover 19 is notelectrostatically attracted to the electrostatic chuck 17. During theplasma process, the cover 19 is urged to the stage 11 side by the seconddrive mechanism 23B, and whereby the contact face 19 d of the annularprotrusion portion 19 c is pressed onto the upper face of theelectrostatic chuck 17.

The present invention is not limited to the configurations in theembodiments, and various modifications are possible.

For example, by raising and lowering the stage 11 with respect to thecover 19 which is fixed in the chamber 3, a configuration that the cover19 comes into and out of contact with the stage 11 can be adopted.

In addition, the present invention is described using a dry etchingapparatus of ICP type as an example, but the present invention can alsobe applied to a dry etching apparatus of parallel-plate type. Inaddition, the present invention can also be applied to other plasmaprocessing apparatuses such as a CVD apparatus limited to the dryetching apparatus.

What is claimed is:
 1. A method for plasma processing a substrate heldby a carrier having a frame and a holding sheet, comprising: loading thecarrier holding the substrate into a chamber of a plasma processingapparatus so that the carrier is placed on an electrode unit of a stage,the electrode unit incorporating (i) a first electrostatic attractionelectrode of unipolar type overlapping the substrate in plan view and(ii) a second electrostatic attraction electrode of bipolar typesurrounding the first electrostatic attraction electrode, the secondelectrostatic attraction electrode overlapping the frame and the holdingsheet between the substrate and the frame in the plan view withoutoverlapping the substrate in plan view; electrostatically attracting thesubstrate by the first electrostatic attraction electrode by applying afirst direct current voltage; electrostatically attracting the frame andthe holding sheet between the substrate and the frame by the secondelectrostatic attraction electrode by applying a second direct currentvoltage; generating plasma in the chamber, thereby plasma processing thesubstrate.
 2. The method according to claim 1, wherein the electrodeunit is cooled.
 3. The method according to claim 2, further comprisingproviding a cover capable of coming into and out of contact with stage,wherein the chamber has a pressure reducible internal space, and whereinthe cover comprises a body covering the holding sheet and the frame ofthe carrier placed on the electrode unit; and a window penetrating thebody in a direction perpendicular to the stage so as to expose thesubstrate held in the carrier placed on the electrode unit to theinternal space.
 4. The method according to claim 3 wherein the firstelectrostatic attraction electrode is incorporated in a first area ofthe electrode unit, the first area being an area in which the substrateis placed via the holding sheet, and wherein the second electrostaticattraction electrode is incorporated in a second area of the electrodeunit, the second area including at least an area in which the frame isplaced via the holding sheet and an area in which the holding sheetbetween the substrate and the frame is placed, and wherein the secondarea includes an area in which the cover abuts on the electrode unit. 5.The method according to claim 3, wherein the first electrostaticattraction electrode is incorporated in a first area of the electrodeunit, the first area being an area in which the substrate is placed viathe holding sheet, wherein the second electrostatic attraction electrodeis incorporated in a second area of the electrode unit, the second areaincluding at least an area in which the frame is placed via the holdingsheet and an area in which the holding sheet between the substrate andthe frame is placed, and wherein the second area does not include anarea in which the cover abuts on the electrode unit, and wherein theplasma processing apparatus further comprises a clamp mechanismconfigured to press the cover onto the stage.
 6. The method according toclaim 1, wherein the first electrostatic attraction electrode has acircular-disc shape with an outer diameter larger than the substrate. 7.The method according to claim 1, wherein the electrode unit furtherincorporating a bias electrode incorporated below the firstelectrostatic attraction electrode, the bias electrode beingelectrically connected to a radio frequency power source, and wherein abias voltage is applied from the radio frequency power source to thebias electrode during plasma processing.
 8. The method according toclaim 7, wherein a distance between the first electrostatic attractionelectrode and a top surface of the electrode unit is smaller than adistance between the bias electrode and the top surface of the electrodeunit.
 9. The method according to claim 1, wherein a voltage obtained bysuperimposing a radio frequency voltage on a direct current voltage isapplied to the first electrostatic attraction electrode.